Polaron Structure and Transport in Fullerene Materials: Insights from First-Principles Calculations

Abstract

Organic semiconductors offer a low-cost alternative to inorganic semiconductors. However, their usefulness is limited by a relatively low mobility of polaron charge carriers. Past research indicates a positive correlation between charge density and charge mobility in organic semiconductors. This relationship is usually attributed to the phenomenon of excess charges filling traps. Here, we explore whether charge density may also affect mobility via influence on intermolecular couplings. Density functional theory (DFT) with a long-range corrected (LC-BLYP) functional is used to calculate charge densities and electronic couplings of negative charges on C70 fullerenes in the presence of nearby negative point charges, which provides an upper limit calculation of the influence of nearby polarons. We find that in C70 systems with relatively low couplings, the presence of additional charges has an effect of maximizing intermolecular couplings and hence transport. This effect drops off quickly with distance, suggesting that it is relevant only at extremely high charge densities that are an unlikely event in current C70 devices. The effect of charge density on couplings may be useful in understanding transport in very limited regions of C70 materials where the local charge density is high; however, it is unlikely to affect overall device performance.

Charge generation in organic photovoltaics: a review of theory and computation

“…Previous work has shown that OPV performance is affected by the relative orientation of donor and acceptor molecules, 123,124,146,211 and charge transport in organic semiconductors is known to be sensitive to small changes in intermolecular orientation. 25,26,212,213 This sensitivity to small changes in orientations is consistent with reports that changes in phase, such as aggregation into a mixed phase, cause changes in excitation energies for both polymers and fullerenes in OPV materials. 142,[214][215][216][217] EPR studies have shown that the electronic structure of C 60 anions is sensitive to geometric distortions, consistent with the sensitivities to geometry that we observe in organic semiconducting devices.…”

“…[19][20][21][22][23] for more detailed discussion of exciton diffusion in OPVs and ref. [24][25][26][27][28] for more discussion of charge transport.…”

Tunable spectra and charge transfer process of benzodifurandione-based polymer by sulfur substitution

“…Conjugated organic polymers, which exhibit a good absorption and emission of light or electricity and photoconductivity, have been widely used in electronic devices such as organic eldeffect transistors (OFETs), 1,2 organic light emitting diodes (OLEDs) 3,4 and organic photovoltaic devices (OPVs). [5][6][7] Compared with the traditional inorganic semiconductor materials, the conjugated organic polymers have many outstanding advantages, such as being low-cost, exible, lightweight materials and having a large-area fabrication. All these merits increase their applicability as active components in organic electronic devices and molecular electronics.…”

Fullerene-Based Photoactive Layers for Heterojunction Solar Cells: Structure, Absorption Spectra and Charge Transfer Process

“…The geometries, electronic structures, polarizabilities and hyperpolarizabilities, and UV-vis spectra of metallo phthalocyanine dyes and metallophthalocyanine-fullerene supramolecules were studied [ 16 ]. The relationship between charge density and mobility of fullerenes was revealed by using first-principles calculation [ 17 ]. Barszcza et al .…”